Numerous applications require knowledge of light intensity. One example is ambient light sensors that measure the amount of light near a portable device, such as a cellular phone, to adjust screen brightness. Another example is motion detection sensors that operate based on measurement of infrared light intensity from people. Image sensors are arrays of individual light sensors that, in some instances, are integrated on a chip. Optical components, such as lenses and mirrors, are often used to map the areal light intensity information onto the image sensors to provide an image of the field of view.
The light intensity may be measured through a variety of techniques. In some embodiments, the light-sensitive area is made from a semiconducting material of proper band-gap whose conductance changes in relation to the light intensity. In some embodiments, the light sensing area is made of a semiconducting material with suitable alternating doping so that a light-sensitive diode or transistor is formed. Some light sensors operate based on the changes in properties of nanoparticles or layers made from them, such as electrical conductance, to extract information about light intensity.
Typical light sensors have a planar structure and produce an electrical signal proportional to the intensity of an incident light beam. Many applications, however, require knowledge of the direction of the incident light beam as well. For example, room occupancy systems often need to monitor the location of infrared light sources (i.e., humans). Portable electronic devices can use directional light sensors to track users' gestures and movements. Two directional light sensors can be employed to estimate the distance to a light source using triangulation.
Extraction of direction information is typically based on a number of individual or integrated light sensors in combination with other discrete elements to provide direction information. In some embodiments, several discrete sensors each facing a different direction are used and the signals from those sensors are combined to extract the direction of light. In other cases, optical components are used to redirect light beams from different directions on one or more planar sensors. In U.S. Published Patent Application No. 2014/0085265 A1, methods are described to estimate the direction of light based on the measured intensity of light on a planar sensor which passes through beam steering elements. In U.S. Pat. No. 8,471,188 B2, a technique is described for estimation of the direction of light from modulated light source using rigidly-mounted sensors on a curved surface or by using a lens over a planar sensor surface. In U.S. Published Patent Application No. 2014/0203391 A1, methods are described to realize light sensors below fixed-angle channels for incident light. The direction of light is then estimated using the relative signal amplitudes from multiple sensors facing different directions.